Antigen receptor present on the surface of bone-marrow derived lymphocytes are thought to play an important role in regulating the immune responses which defends us from various infectious diseases, autoimmune disease as well as cancers. Previous studies by other laboratories revealed that an IgM class antigen receptor is a monomeric IgM protein that extends its antigen-binding sites to outside of cells. The basic questions we ask are: 1) What are the structural and functional differences between such receptor IgM and antibody IgM secreted from antibody-forming cells?; and 2) How are receptor IgM proteins anchored in the plasma membrane of B lymphocytes? Our approach to these questions are: 1) to isolate and characterize surface IgM from detergent-treated chronic lymphocytic lymphocytes as well as EBV-transformed B cells; 2) to examine the molecular nature of surface IgM released from the cell surface by reduction of viable B cells; and 3) to investigate the characteristics of 8S IgM shed from the cell surface into plasma. Furthermore, attempts will be made to biochemically and biologically characterize an anchoring molecule that may be present in the detergent-solubilized but not in the reduction-solubilized surface IgM.